It happened again just now. From the trace it looks like it was when I searched for "gedit" in the overview - which has a snap result AFAIK.

Thread 5 (Thread 0x7f1cadf5e700 (LWP 8464)):
#0  0x00007f1cd4318cdd in poll () at ../sysdeps/unix/syscall-template.S:84
#1  0x00007f1cd72ac119 in g_main_context_poll (priority=<optimised out>, n_fds=2, fds=0x7f1ca050f2f0, timeout=<optimised out>, context=0x7f1ca049a910) at ../../../../glib/gmain.c:4187
#2  0x00007f1cd72ac119 in g_main_context_iterate (context=0x7f1ca049a910, block=block@entry=1, dispatch=dispatch@entry=1, self=<optimised out>) at ../../../../glib/gmain.c:3881
#3  0x00007f1cd72ac4b2 in g_main_loop_run (loop=0x7f1ca04395b0) at ../../../../glib/gmain.c:4082
#4  0x00007f1cb04f8b26 in end_sync (data=0x7f1cadf5d8b0, data=0x7f1cadf5d8b0) at snapd-client.c:2446
#5  0x00007f1cb04f8b26 in snapd_client_find_section_sync (client=0x55a0f05ef960 [SnapdClient], flags=flags@entry=SNAPD_FIND_FLAGS_NONE, section=section@entry=0x0, query=query@entry=0x7f1ca061edd0 "ged", suggested_currency=suggested_currency@entry=0x0, cancellable=cancellable@entry=0x55a0f066d840 [GCancellable], error=0x7f1cadf5d9d8) at snapd-client.c:3798
#6  0x00007f1cb071424f in find_snaps (plugin=plugin@entry=0x55a0f06051d0 [GsPlugin], flags=flags@entry=SNAPD_FIND_FLAGS_NONE, section=section@entry=0x0, query=query@entry=0x7f1ca061edd0 "ged", cancellable=0x55a0f066d840 [GCancellable], error=error@entry=0x7f1cadf5d9d8) at ../plugins/snap/gs-plugin-snap.c:231
#7  0x00007f1cb0714e40 in gs_plugin_add_search (plugin=0x55a0f06051d0 [GsPlugin], values=<optimised out>, list=0x55a0f2536d00 [GsAppList], cancellable=<optimised out>, error=0x7f1cadf5d9d8)
    at ../plugins/snap/gs-plugin-snap.c:505
#8  0x000055a0ef18d7cf in gs_plugin_loader_call_vfunc (helper=helper@entry=0x55a0f0ffe300, plugin=plugin@entry=0x55a0f06051d0 [GsPlugin], app=app@entry=0x0, list=0x55a0f2536d00 [GsAppList], 
    list@entry=0x0, cancellable=cancellable@entry=0x55a0f066d840 [GCancellable], error=error@entry=0x7f1cadf5dae8) at ../lib/gs-plugin-loader.c:657
#9  0x000055a0ef18db1d in gs_plugin_loader_run_results (helper=helper@entry=0x55a0f0ffe300, cancellable=cancellable@entry=0x55a0f066d840 [GCancellable], error=error@entry=0x7f1cadf5dae8) at ../lib/gs-plugin-loader.c:1083
#10 0x000055a0ef18f32a in gs_plugin_loader_process_thread_cb (task=0x7f1ca0006ab0 [GTask], object=0x7f1cbc004320, task_data=0x55a0f0ffe300, cancellable=0x55a0f066d840 [GCancellable]) at ../lib/gs-plugin-loader.c:3054
#11 0x00007f1cd6f52b76 in g_task_thread_pool_thread (thread_data=0x7f1ca0006ab0, pool_data=<optimised out>) at ../../../../gio/gtask.c:1328
#12 0x00007f1cd72d3ff0 in g_thread_pool_thread_proxy (data=<optimised out>) at ../../../../glib/gthreadpool.c:307
#13 0x00007f1cd72d3625 in g_thread_proxy (data=0x55a0f05e8a80) at ../../../../glib/gthread.c:784
#14 0x00007f1cd45e874a in start_thread (arg=0x7f1cadf5e700) at pthread_create.c:456
#15 0x00007f1cd4324caf in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:97


● snapd.service - Snappy daemon
   Loaded: loaded (/lib/systemd/system/snapd.service; enabled; vendor preset: enabled)
   Active: active (running) since Tue 2017-09-19 09:13:12 BST; 47min ago

Maybe it started happening then? The logs from the journal say..

Sep 19 09:13:11 nightingale snapd[2306]: error: cannot gracefully finish, still active connections on /run/snapd.socket after 5s
Sep 19 09:13:11 nightingale systemd[1]: snapd.service: Main process exited, code=exited, status=1/FAILURE
Sep 19 09:13:11 nightingale systemd-logind[2283]: Got message type=signal sender=:1.0 destination=n/a object=/org/freedesktop/systemd1 interface=org.freedesktop.DBus.Properties member=PropertiesChanged cookie=2550 reply_cookie=0 error=n/a
Sep 19 09:13:11 nightingale systemd[1]: snapd.service: Unit entered failed state.
Sep 19 09:13:11 nightingale systemd[1]: snapd.service: Failed with result 'exit-code'.
Sep 19 09:13:11 nightingale systemd-logind[2283]: Got message type=signal sender=:1.0 destination=n/a object=/org/freedesktop/systemd1 interface=org.freedesktop.DBus.Properties member=PropertiesChanged cookie=2551 reply_cookie=0 error=n/a
Sep 19 09:13:11 nightingale systemd-logind[2283]: Got message type=signal sender=:1.0 destination=n/a object=/org/freedesktop/systemd1/unit/snapd_2eservice interface=org.freedesktop.DBus.Properties member=PropertiesChanged cookie=2552 reply_cookie=0 error=n/a
Sep 19 09:13:11 nightingale systemd-logind[2283]: Got message type=signal sender=:1.0 destination=n/a object=/org/freedesktop/systemd1/unit/snapd_2eservice interface=org.freedesktop.DBus.Properties member=PropertiesChanged cookie=2553 reply_cookie=0 error=n/a
Sep 19 09:13:11 nightingale systemd-logind[2283]: Got message type=signal sender=:1.0 destination=n/a object=/org/freedesktop/systemd1/unit/snapd_2esocket interface=org.freedesktop.DBus.Properties member=PropertiesChanged cookie=2554 reply_cookie=0 error=n/a
Sep 19 09:13:11 nightingale systemd-logind[2283]: Got message type=signal sender=:1.0 destination=n/a object=/org/freedesktop/systemd1/unit/snapd_2esocket interface=org.freedesktop.DBus.Properties member=PropertiesChanged cookie=2555 reply_cookie=0 error=n/a
Sep 19 09:13:11 nightingale systemd[1]: snapd.service: Service hold-off time over, scheduling restart.
Sep 19 09:13:11 nightingale systemd[1]: Stopped Snappy daemon.
Sep 19 09:13:11 nightingale systemd[1]: Starting Snappy daemon...